The present invention relates to a non-reciprocal circuit device employed for mobile communications equipment including a automobile phone and a cellular phone used in ultrahigh or microwave frequency bands, more particularly, relates to a non-reciprocal circuit device capable of handling high electric power.
Manufacturers have long recognized the merit of a non-reciprocal circuit device because of its compact structure, and have used it in a terminal for mobile communications.
In the non-reciprocal circuit device, as shown in FIG. 9, a signal entered from an input terminal, which travels in a forward direction, passes through a low-loss route to an output terminal. On the other hand, as shown in FIG. 10, a signal entered from an output terminal, which travels in a reverse direction, passes through a route different from aforementioned one and reaches a different terminal, at which the signal is absorbed in a termination resistor connected with the terminal. That is, the non-reciprocal circuit device has the characteristics: if an output terminal reflects signals entered from an input terminal, very few of the signals return to the input terminal. In a transmission stage of mobile communications equipment, a non-reciprocal circuit device is placed between a power amplifier and an antenna. This arrangement is useful to avoid that reflected waves from the antenna flow back into the power amplifier, or to stabilize the load impedance of the power amplifier.
FIG. 11 shows a typical structure of the non-reciprocal circuit device that has been widely used in a terminal for a cellular phone terminal.
Here will be briefly described the structure with reference to the accompanying drawings.
Magnetic circular plate 55 is made of ferrite and is disposed facing magnet 52, so that an appropriate direct-current magnetic field can be applied to plate 55. Under the arrangement, plate 55 exhibits anisotropic behavior for a radio frequency (rf) electromagnetic field. Three strip-lines 54a, 54b, and 54c are disposed adjacent to magnetic circular plate 55 in such a manner that each strip-line lies on another to cross each other at an angle of approximately 120xc2x0. Each of the strip-lines is electrically insulated by insulating sheet 56. Ends 54d and 54e of strip-lines 54a and 54b are connected to input terminal 53a and output terminal 53b, respectively, of terminal base 53. At the same time, ends 54d and 54e connect through matching capacitors 58a and 58b, respectively, to the ground. One end of strip-line 54c connects through the parallel arrangement of matching capacitor 58c and termination resistor 57 to the ground.
Other ends of each strip-line connected to a circular ground-plate (not shown) are further electrically connected, together with impedance-matching capacitors 58a, 58b, 58c and the ground-side electrodes of termination resistor 57, to lower case 59 and are grounded. Magnetic circular plate 55 and magnet 52 covered with upper case 51 and lower case 59 form into a magnetic circuit.
In the non-reciprocal circuit device having the structure above, a radio frequency signal entered from input terminal 53a travels through strip-line 54a, plate 55, and strip-line 54b to output terminal 53b as an output signal with low-loss. On the other hand, an rf-signal entered from output terminal 53b travels through strip-line 54b, plate 55, and strip-line 54c to terminal 54f The rf-signals, due to its traveling in a reverse direction, are absorbed by termination resistor 57, so that there are few to back to input terminal 53a. The non-reciprocal circuit device thus exhibits the irreversible behavior.
As the recent widespread use of mobile communications, mobile communications equipment has been showing size and cost reductions, at the same time, consuming higher power. This trend is also true for base stations: the non-reciprocal circuit device used for a base station is often operated at around maximum power rating. With the prior-art structure, however, the non-reciprocal circuit device is overheated by a surge of high power. Countermeasures against the undesired heat, for example, are disclosed in Japanese Patent Laid-open No. H02-55403 and H10-261904: in the former one, two or more film-resistors are used as a resistor to distribute the heat; in the latter, two or more chip resistors are used as a resistor and heat generated at the chip resistors is transferred from the ground-side terminal of the chip resistors to the case. In either method, however, the temperature of the resistor still reaches extremely high when high power surges into the resistor.
It is therefore the object of the present invention to provide a high-power and small-sized non-reciprocal circuit device without impairment of the capability.
According to the present invention, non-reciprocal circuit device includes: a magnetic substrate; a magnet applying a magnetic field to the substrate; strip-lines disposed in a crossing arrangement at an angle with each other on the substrate, with each strip-line electrically insulated; capacitors connected to the strip-lines; a termination resistor connected to one of the strip-lines; a case accommodating the components above; and a thermal conductor disposed in the case. In the non-reciprocal circuit device, the thermal conductor radiates heat generated in at least one of the termination resistor and the strip-lines.
It is thus possible to provide a high-power acceptable non-reciprocal circuit device, without impairment of the advantagesxe2x80x94having a shrunk body with low-loss.
Furthermore, the non-reciprocal circuit device has the merits listed below:
(1) transferring at least a part of heat generated at the termination resistor or the stlip-lines, through the thermal conductor, to at least a part of the component can bring effective heat-radiation.
(2) forming an insulating material into the thermal conductor allows the conductor to come in contact with a conductive componentxe2x80x94this increases design flexibility.
(3) disposing the thermal conductor close to, or in contact with the termination resistor or the stlip-lines can bring more effective heat-radiation.
(4) forming a material having flexibility or elasticity into the thermal conductor allows the conductor to be altered into a desired shape to fit within the case, which brings an intimate contact between the circuit components, with the result of obtaining effective heat-radiation. In addition, a step of adjusting the spacing between the components can be eliminated from assembly work, thereby increasing productivity.
(5) forming a resin material into the thermal conductor allows the conductor to be easily and properly housed into the case with no ill effect on electric characteristics. At the same time, such a material enhances fire retardation of the structure.
(6) forming thickly the thermal conductor on the termination resistor allows the conductor to have greater heat capacity, thereby offering effective heat-radiation.
(7) disposing the thermal conductor so as to make contact with the magnet or a part of the case can transfer heat through the case having a greater heat-radiation effect.
(8) forming an adhesive material into the thermal conductor allows the conductor to be fixed in the case.
(9) forming a solid or properly viscous material into the thermal conductor protects the conductor from being extruded from the case, thereby having no ill effect on other circuits.
(10) disposing, in the case, the terminal base that contains at least input and output terminals and a portion accommodating the substrate, and that has a structure keeping the termination resister exposedxe2x80x94this will make positioning of the substrate and mounting of the thermal conductor really simple.
(11) forming the terminal base into a shape having an opening in part, that is, into the general shape of xe2x80x9cCxe2x80x9d, and placing the substrate at the central part of the xe2x80x9cCxe2x80x9dxe2x80x94this will easily keep room for mounting two or more termination resistors and for disposing the thermal conductor therein.
(12) determining the volume of the insulating thermal conductor in the range from 2% to 75% of the volume of the case offers good heat-radiation effect.
(13) filling spaces of the case with the thermal conductor increases the heat-radiation effect.